"You'll pass" is not an arrangement or an intention. Ann is just saying what will happen or what she thinks will happen; she is predicting the future. When we predict a future happening or a future situation, we use will/won't.

When you return home, you'll notice a lot of changes.

This time next year I'll be in Japan. Where will you be?

When will you find out your exam results?

Tom won't pass his exam. He hasn't done any work for it.

We often use will with these words and expressions:

probably I'll probably be a little late this evening.(I'm) sure You must meet Ann. I'm sure you'll like her.(I) bet I bet Carol will get the job.(I) think Do you think we'll win the match?(I) suppose I suppose we'll see John at the party.(I) guess I guess I'll see you next week.

Will and shall
You can say I will or I shall (I'll)

we will or we shall (we'll)

I will (orI shall) probably go to Europe this summer.

We will (orwe shall) probably go to Europe this summer.

Will is more common than shall. In speech we normally use the short forms I'll and we'll: